Electromagnetic interference

“ With the large condensers and self-inductances employed in modern cable telegraphy, it is easy to get a series of beautifully regular and gradually damped electric oscillations, with a period of two or three seconds, recorded by an ordinary signalling instrument or siphon recorder.
These electromagnetic waves in space have been known on the side of theory ever since 1865, but interest in them was immensely quickened by the discovery of a receiver or detector for them. ”

“ Although radio frequency emissions are usually harmless, there are still certain safety precautions you should follow whenever you are near high-power rf sources. Normally, electromagnetic radiation from transmission lines and antennas isn't strong enough to electrocute personnel. However, it may lead to other accidents and can compound injuries. Voltages may be induced into metal objects both above and below ground, such as wire guys, wire cable, hand rails, and ladders. ”

“ RADIATION RESISTANCE—The resistance, which if inserted in place of an antenna, would consume the same amount of power as that radiated by the antenna.
RADIO FREQUENCIES—Electromagnetic frequencies that fall between 3 kilohertz and 300 gigahertz and are used for radio communications.
RADIO HORIZON—The boundary beyond the natural horizon in which radio waves cannot be propagated over the earth’s surface.
RADIO WAVE— (1) A form of radiant energy that can neither be seen nor felt; (2) An electromagnetic wave generated by a transmitter. ”

“ Electrical energy from the transmitter is converted into electromagnetic energy by the antenna and radiated into space. On the receiving end, electromagnetic energy is converted into electrical energy by the antenna and fed into the receiver.
The electromagnetic radiation from an antenna is made up of two components, the E field and the H field. The total energy in the radiated wave remains constant in space except for some absorption of energy by the earth. However, as the wave advances, the energy spreads out over a greater area. ”

“ The electromagnetic waves have the power of exciting oscillations in a conductor on which they impinge. This is made use of for the purpose of receiving the messages. When the waves strike the aerial of a distant station they set up high frequency oscillations, which are usually too weak to make their presence known except with the aid of a sensitive device, called a detector. ”

“ Many waveguide devices have been developed, however, that modify the energy in some fashion during the transmission. Some devices do nothing more than change the direction of the energy. Others have been designed to change the basic characteristics or power level of the electromagnetic energy. ”

“ To further realize, let the field terminate internally at r=a, giving a cylindrical-surface distribution of electrification, and terminate the tubes of displacement externally upon a coaxial cylindrical surface; we then produce a real electromagnetic plane wave with electrification, and of finite energy. We have supposed the electrification to be carried through the dielectric at speed ν, to keep up with the wave, which would of course break up if the charge were stopped. ”

“ The radiation field is made up of magnetic and electric lines of force that are always at right angles to each other. Most electromagnetic fields in space are said to be linearly polarized. The direction of polarization is the direction of the electric vector. That is, if the electric lines of force (E lines) are horizontal, the wave is said to be horizontally polarized (fig. 2-2) , and if the E lines are vertical, the wave is said to be vertically polarized. Since the electric field is parallel to the axis of the dipole, the antenna is in the plane of polarization. ”

“ The Ionosphere and Radio Waves When a radio wave encounters a particle having an electric charge, it causes that particle to vibrate. The vibrating particle absorbs electromagnetic energy from the radio wave and radiates it. The net effect is a change of polarization and an alteration of the path of the wave. That portion of the wave in a more highly ionized region travels faster, causing the wave front to tilt and the wave to be directed toward a region of less intense ionization. ”

“ Various factors in the antenna circuit affect the radiation of electromagnetic energy. In figure 2-3, for example, if an alternating current is applied to the A end of wire antenna AB, the wave will travel along the wire until it reaches the B end. Since the B end is free, an open circuit exists and the wave cannot travel further. This is a point of high impedance. ”

“ In a way, it works. The spring acts as an aerial and picks up more of the beam than my hand. But I tried to make a Faraday cage. That will stop most electromagnetic radiation, but not this stuff! It goes right through, like electrons through a radio tube grid. ”

“ Electromagnetic energy is often passed through a waveguide to transfer the energy from a source into space. As previously mentioned, the impedance of a waveguide does not match the impedance of space, and without proper impedance matching standing waves cause a large decrease in the efficiency of the waveguide. ”

“ Except for this very special case, it is easy to see that the electromagnetic conception requires a major overhaul of the notion of world. The equations of electromagnetism imply, in their usual form, that an electromagnetic disturbance, e.g. a light wave, propagates in vacuum with the same velocity in all directions, equal to three hundred thousand kilometers per second. ”

“ Interference can not be overcome by any such methods as were proposed. The truth is this: in the air the potential increases at the rate of about fifty volts per foot of elevation, owing to which there may be a difference of pressure amounting to twenty, or even forty thousand volts between the upper and lower ends of the antenna. The masses of the charged atmosphere are constantly in motion and give up electricity to the conductor, not continuously but rather disruptively, this producing a grinding noise in a sensitive telephonic receiver. ”

“ INCIDENT WAVE— (1) The wave that strikes the surface of a medium; (2) The wave that travels from the sending end to the receiving end of a transmission line.
INDUCTION FIELD—The electromagnetic field produced about an antenna when current and voltage are present on the same antenna.
INDUCTION LOSSES—The losses that occur when the electromagnetic field around a conductor cuts through a nearby metallic object and induces a current into that object. ”

“ Each time you insert the plug into a new circuit, you will blow out a fuse and silence all radios running on power from that circuit until a new fuse is put in.
(3) Damaging insulation on any electrical equipment tends to create radio interference in the immediate neighborhood, particularly on large generators, neon signs, fluorescent lighting, X-ray machines, and power lines. If workmen can damage insulation on a high tension line near an enemy airfield, they will make ground-to-plane radio communications difficult and perhaps impossible during long periods of the day. ”

“ Aerial transmission lines are exposed to direct discharges of lightning, to electromagnetic charges due to lightning discharges near by, and to electrostatic charges that are brought about by contact with or induction from electrically charged bodies of air. ”

“ In general, atmospheric absorption increases with frequency. It is a problem only in the SHF and EHF frequency range. At these frequencies, attenuation is further increased by scattering due to reflection by oxygen, water vapor, water droplets, and rain in the atmosphere.
1010. Noise Unwanted signals in a receiver are called interference. The intentional production of such interference to obstruct communication is called jamming. Unintentional interference is called noise. ”

“ This approximation will be broken at low concentration of the active centers, as well as at the excitation with very strong and short pulses. In both cases, the different sites interact with electromagnetic field faster than they exchange the energy. ”

“ This, then, is a force acting on a body caused by its motion through the electromagnetic field, or by changes occurring in that field itself; and the effect of the force is either to produce a current and heat the body, or to decompose the body, or, when it can do neither, to put the body in a state of electric polarization, - a state of constraint in which opposite extremities are oppositely electrified, and from which the body tends to relieve itself as soon as the disturbing force is removed. ”

“ WAVEGUIDE THEORY
The two-wire transmission line used in conventional circuits is inefficient for transferring electromagnetic energy at microwave frequencies. At these frequencies, energy escapes by radiation because the fields are not confined in all directions, as illustrated in figure 3-15. Coaxial lines are more efficient than two-wire lines for transferring electromagnetic energy because the fields are completely confined by the conductors, as illustrated in figure 3-16. Waveguides are the most efficient way to transfer electromagnetic energy. ”

“ The molecules vibrate in tune, at terrific frequency, and the light can pass perfectly. What will happen, however, if someone locates the source of the radio waves? It'll be simple for them to send out a radio beam and touch our invisible ship with it. The two radio waves impressed on us now will be out of step and the interference will instantly make us visible. We can no longer attack them with our atomic hydrogen blast, or with the gas—both are useless unless we can get close to them, and we can't come within ten miles of them now. Those bombs of theirs are effective at that distance. ”

“ To avoid such interference the telephone-wires if suspended in the air require to be placed at some distance from telegraphic line wires, and to be supported by separate posts. Another way of neutralizing interference consists in twisting two separately insulated telephone-wires together, so as to form a strand, and in using the two conductors as a metallic circuit to the exclusion of the earth; the working current will, in that case, receive equal and opposite inductive influences, and will, therefore, remain unaffected by them. ”

“ But if perfectly conducting surfaces be given on which to terminate the displacement, the natural motion of the wave will itself carry the electrification along them. In fact we now have the rudimentary telegraph-circuit, with no allowance made for absorption of energy in the wires, and the consequent distortion. If the conductors be not coaxial, we only alter the distribution of the displacement and induction, without affecting the propagation without distortion. ”

“ Crowninshield.
"We are running up our meters in order to catch the higher tuned waves," Bob added. "That is part of the bedlam."
"And the rest?"
"It is static interference."
"What's that?"
"Well, static is the big bugbear of radio," answered Bob, pausing a moment in regulating his tuner and detector. "It is caused by stray waves moving in various directions through the atmosphere, and by electrical conditions. It is the defect all wireless people have to fight. Sometimes it is worse than others and unfortunately to-night it promises to be pretty bad. ”

“ The general equations are next applied to the case of a magnetic disturbance propagated through a non-conductive field, and it is shown that the only disturbances which can be so propagated are those which are transverse to the direction of propagation, and that the velocity of propagation is the velocity v, found from experiments such as those of Weber, which expresses the number of electrostatic units of electricity which are contained in one electromagnetic unit.
This velocity is so nearly that of light, that it seems we have strong reason to conclude that light itself ”

“ I ultimately succeeded in constructing a few instruments with which I was able to obtain the values of the indices of refraction of various substances for electric waves, the wave-length of electric radiation, to demonstrate the phenomena of double refraction and polarization of the electric rays, and to find out certain substances which act as electric tourmalines. The simplified apparatus with which many of the properties of electromagnetic radiation may be studied is here exhibited. ”

“ When, however, the main current attempts to flow across, phenomena of electromagnetic repulsion force the arc upward along the horns, lengthening and attenuating it, until it finally becomes extinguished.
Ques. How should lightning arresters be grounded?
Ans. They should be connected to ground with No. 6 B. & S. gauge copper wire or larger. Gas pipes within a building must not be used for a ground connection. 891
Fig. ”

“ We generate a signal, vary the frequency until I lose my mutant powers—and that's it! We generate as strong a signal as we can. Then we have every transmitter in the country put on a direct line to us. When the radar spots the first saucer, we let go with every kilowatt of power we've got. ”

“ The agreement of the results seems to show that light and magnetism are affections of the same substance, and that light is an electromagnetic disturbance propagated through the field according to electromagnetic laws. ”

“ Interfere with the frequency that closes our bridges, I mean. It's the same principle as concussion affecting the displacement area."
"Wait a minute. Okay, go on. I'm recording this, now."
"If our television and radio transmitters will handle the signal, we can blanket the whole planet with interference. Any mutant that hits it will automatically be deprived of his mutant powers."
"What...?"
"Look. We can make the whole first wave human normals. The Army can round them up and keep them unconscious while we adjust our interference to meet the second wave." ”